Lizmat's mystery oneliner bug

gistfile1.txt

dogbert@dogbert-VirtualBox:~$ MVM_SPESH_DISABLE=1 perl6 --ll-exception -e 'my %h = "a" .. "e" Z=> 1..5; for %h.keys { %h{$_~$_} = 42 }'
concatenate requires a concrete string, but got null
   at SETTING::src/core.c/Str.pm6:3669  (/home/dogbert/.rakudobrew/versions/moar-master/install/share/perl6/runtime/CORE.c.setting.moarvm:infix:<~>)
 from -e:1  (<ephemeral file>:)
 from -e:1  (<ephemeral file>:<unit>)
 from -e:1  (<ephemeral file>:<unit-outer>)
 from gen/moar/stage2/NQPHLL.nqp:1946  (/home/dogbert/.rakudobrew/versions/moar-master/install/share/nqp/lib/NQPHLL.moarvm:eval)
 from gen/moar/stage2/NQPHLL.nqp:2056  (/home/dogbert/.rakudobrew/versions/moar-master/install/share/nqp/lib/NQPHLL.moarvm:)
 from gen/moar/stage2/NQPHLL.nqp:2111  (/home/dogbert/.rakudobrew/versions/moar-master/install/share/nqp/lib/NQPHLL.moarvm:command_eval)
 from gen/moar/Compiler.nqp:109  (/home/dogbert/.rakudobrew/versions/moar-master/install/share/perl6/lib/Perl6/Compiler.moarvm:command_eval)
 from gen/moar/stage2/NQPHLL.nqp:2036  (/home/dogbert/.rakudobrew/versions/moar-master/install/share/nqp/lib/NQPHLL.moarvm:command_line)
 from gen/moar/rakudo.nqp:127  (/home/dogbert/.rakudobrew/versions/moar-master/install/share/perl6/runtime/perl6.moarvm:MAIN)
 from gen/moar/rakudo.nqp:1  (/home/dogbert/.rakudobrew/versions/moar-master/install/share/perl6/runtime/perl6.moarvm:<mainline>)
 from <unknown>:1  (/home/dogbert/.rakudobrew/versions/moar-master/install/share/perl6/runtime/perl6.moarvm:<main>)
 from <unknown>:1  (/home/dogbert/.rakudobrew/versions/moar-master/install/share/perl6/runtime/perl6.moarvm:<entry>)



dogbert@dogbert-VirtualBox:~$ perl6-valgrind-m -e 'my %h = "a" .. "e" Z=> 1..5; for %h.keys { %h{$_~$_} = 42 }'
================================================================================================
This is Rakudo running in valgrind, a tool for debugging and profiling programs.
Running a program in valgrind usually takes *a lot* more time than running it directly,
so please be patient.
Valgrind options can be added with MVM_VALGRIND_OPTS environment variable.

This Rakudo version is 2021.03.174.g.596.ccef.3.b built on MoarVM version 2021.03.39.gba.124.ad.12,
running on linuxmint (20.Ulyana) / linux
------------------------------------------------------------------------------------------------
==1558167== Memcheck, a memory error detector
==1558167== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==1558167== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==1558167== Command: /home/dogbert/.rakudobrew/versions/moar-master/install/bin/rakudo-m -e my\ %h\ =\ "a"\ ..\ "e"\ Z=\>\ 1..5;\ for\ %h.keys\ {\ %h{$_~$_}\ =\ 42\ }
==1558167== 
==1558167== Conditional jump or move depends on uninitialised value(s)
==1558167==    at 0x4B1ED02: MVM_string_check_arg (ops.h:38)
==1558167==    by 0x4B1ED02: MVM_string_concatenate (ops.c:855)
==1558167==    by 0x4A54E2B: MVM_interp_run (interp.c:1603)
==1558167==    by 0x1098E7: main (in /home/dogbert/.rakudobrew/versions/moar-master/install/bin/rakudo-m)
==1558167== 
==1558167== Conditional jump or move depends on uninitialised value(s)
==1558167==    at 0x51A61C2: __vfprintf_internal (vfprintf-internal.c:1688)
==1558167==    by 0x51BB119: __vsnprintf_internal (vsnprintf.c:114)
==1558167==    by 0x4A48FE6: vsnprintf (stdio2.h:80)
==1558167==    by 0x4A48FE6: MVM_exception_throw_adhoc_free_va (exceptions.c:945)
==1558167==    by 0x4A492B1: MVM_exception_throw_adhoc (exceptions.c:898)
==1558167==    by 0x4B18828: MVM_string_check_arg.part.0 (ops.h:39)
==1558167==    by 0x4B1F6E4: MVM_string_check_arg (ops.c:823)
==1558167==    by 0x4B1F6E4: MVM_string_concatenate (ops.c:855)
==1558167==    by 0x4A54E2B: MVM_interp_run (interp.c:1603)
==1558167==    by 0x1098E7: main (in /home/dogbert/.rakudobrew/versions/moar-master/install/bin/rakudo-m)
==1558167== 
==1558167== Use of uninitialised value of size 8
==1558167==    at 0x483EF46: strlen (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==1558167==    by 0x51A7E94: __vfprintf_internal (vfprintf-internal.c:1688)
==1558167==    by 0x51BB119: __vsnprintf_internal (vsnprintf.c:114)
==1558167==    by 0x4A48FE6: vsnprintf (stdio2.h:80)
==1558167==    by 0x4A48FE6: MVM_exception_throw_adhoc_free_va (exceptions.c:945)
==1558167==    by 0x4A492B1: MVM_exception_throw_adhoc (exceptions.c:898)
==1558167==    by 0x4B18828: MVM_string_check_arg.part.0 (ops.h:39)
==1558167==    by 0x4B1F6E4: MVM_string_check_arg (ops.c:823)
==1558167==    by 0x4B1F6E4: MVM_string_concatenate (ops.c:855)
==1558167==    by 0x4A54E2B: MVM_interp_run (interp.c:1603)
==1558167==    by 0x1098E7: main (in /home/dogbert/.rakudobrew/versions/moar-master/install/bin/rakudo-m)
==1558167== 
==1558167== Use of uninitialised value of size 8
==1558167==    at 0x483EF54: strlen (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==1558167==    by 0x51A7E94: __vfprintf_internal (vfprintf-internal.c:1688)
==1558167==    by 0x51BB119: __vsnprintf_internal (vsnprintf.c:114)
==1558167==    by 0x4A48FE6: vsnprintf (stdio2.h:80)
==1558167==    by 0x4A48FE6: MVM_exception_throw_adhoc_free_va (exceptions.c:945)
==1558167==    by 0x4A492B1: MVM_exception_throw_adhoc (exceptions.c:898)
==1558167==    by 0x4B18828: MVM_string_check_arg.part.0 (ops.h:39)
==1558167==    by 0x4B1F6E4: MVM_string_check_arg (ops.c:823)
==1558167==    by 0x4B1F6E4: MVM_string_concatenate (ops.c:855)
==1558167==    by 0x4A54E2B: MVM_interp_run (interp.c:1603)
==1558167==    by 0x1098E7: main (in /home/dogbert/.rakudobrew/versions/moar-master/install/bin/rakudo-m)
==1558167== 
==1558167== Conditional jump or move depends on uninitialised value(s)
==1558167==    at 0x51C1243: _IO_default_xsputn (genops.c:393)
==1558167==    by 0x51C1243: _IO_default_xsputn (genops.c:370)
==1558167==    by 0x51A627B: __vfprintf_internal (vfprintf-internal.c:1688)
==1558167==    by 0x51BB119: __vsnprintf_internal (vsnprintf.c:114)
==1558167==    by 0x4A48FE6: vsnprintf (stdio2.h:80)
==1558167==    by 0x4A48FE6: MVM_exception_throw_adhoc_free_va (exceptions.c:945)
==1558167==    by 0x4A492B1: MVM_exception_throw_adhoc (exceptions.c:898)
==1558167==    by 0x4B18828: MVM_string_check_arg.part.0 (ops.h:39)
==1558167==    by 0x4B1F6E4: MVM_string_check_arg (ops.c:823)
==1558167==    by 0x4B1F6E4: MVM_string_concatenate (ops.c:855)
==1558167==    by 0x4A54E2B: MVM_interp_run (interp.c:1603)
==1558167==    by 0x1098E7: main (in /home/dogbert/.rakudobrew/versions/moar-master/install/bin/rakudo-m)
==1558167== 
==1558167== Use of uninitialised value of size 8
==1558167==    at 0x51C12B0: _IO_default_xsputn (genops.c:394)
==1558167==    by 0x51C12B0: _IO_default_xsputn (genops.c:370)
==1558167==    by 0x51A627B: __vfprintf_internal (vfprintf-internal.c:1688)
==1558167==    by 0x51BB119: __vsnprintf_internal (vsnprintf.c:114)
==1558167==    by 0x4A48FE6: vsnprintf (stdio2.h:80)
==1558167==    by 0x4A48FE6: MVM_exception_throw_adhoc_free_va (exceptions.c:945)
==1558167==    by 0x4A492B1: MVM_exception_throw_adhoc (exceptions.c:898)
==1558167==    by 0x4B18828: MVM_string_check_arg.part.0 (ops.h:39)
==1558167==    by 0x4B1F6E4: MVM_string_check_arg (ops.c:823)
==1558167==    by 0x4B1F6E4: MVM_string_concatenate (ops.c:855)
==1558167==    by 0x4A54E2B: MVM_interp_run (interp.c:1603)
==1558167==    by 0x1098E7: main (in /home/dogbert/.rakudobrew/versions/moar-master/install/bin/rakudo-m)
==1558167== 
==1558167== Use of uninitialised value of size 8
==1558167==    at 0x51C12BE: _IO_default_xsputn (genops.c:393)
==1558167==    by 0x51C12BE: _IO_default_xsputn (genops.c:370)
==1558167==    by 0x51A627B: __vfprintf_internal (vfprintf-internal.c:1688)
==1558167==    by 0x51BB119: __vsnprintf_internal (vsnprintf.c:114)
==1558167==    by 0x4A48FE6: vsnprintf (stdio2.h:80)
==1558167==    by 0x4A48FE6: MVM_exception_throw_adhoc_free_va (exceptions.c:945)
==1558167==    by 0x4A492B1: MVM_exception_throw_adhoc (exceptions.c:898)
==1558167==    by 0x4B18828: MVM_string_check_arg.part.0 (ops.h:39)
==1558167==    by 0x4B1F6E4: MVM_string_check_arg (ops.c:823)
==1558167==    by 0x4B1F6E4: MVM_string_concatenate (ops.c:855)
==1558167==    by 0x4A54E2B: MVM_interp_run (interp.c:1603)
==1558167==    by 0x1098E7: main (in /home/dogbert/.rakudobrew/versions/moar-master/install/bin/rakudo-m)
==1558167== 
concatenate requires a concrete string, but got null
  in block <unit> at -e line 1

==1558167== 
==1558167== HEAP SUMMARY:
==1558167==     in use at exit: 60,799,646 bytes in 210,667 blocks
==1558167==   total heap usage: 269,042 allocs, 58,375 frees, 111,162,864 bytes allocated
==1558167== 
==1558167== LEAK SUMMARY:
==1558167==    definitely lost: 0 bytes in 0 blocks
==1558167==    indirectly lost: 0 bytes in 0 blocks
==1558167==      possibly lost: 1,966,000 bytes in 414 blocks
==1558167==    still reachable: 58,833,646 bytes in 210,253 blocks
==1558167==         suppressed: 0 bytes in 0 blocks
==1558167== Rerun with --leak-check=full to see details of leaked memory
==1558167== 
==1558167== Use --track-origins=yes to see where uninitialised values come from
==1558167== For lists of detected and suppressed errors, rerun with: -s
==1558167== ERROR SUMMARY: 12 errors from 7 contexts (suppressed: 0 from 0)